Reversible, Metal-Free Hydrogen Activation

Although reversible covalent activation of molecular hydrogen (H₂) is a common reaction at transition metal centers, it has proven elusive in compounds of the lighter elements. We report that the compound (C₆H₂Me₃)₂PH(C₆F₄)BH(C₆F₅)₂ (Me, methyl), which we derived through an unusual reaction involving dimesitylphosphine substitution at a para carbon of tris(pentafluorophenyl) borane, cleanly loses H₂ at temperatures above 100°C. Preliminary kinetic studies reveal this process to be first order. Remarkably, the dehydrogenated product (C₆H₂Me₃)₂P(C₆F₄)B(C₆F₅)₂ is stable and reacts with 1 atmosphere of H₂ at 25°C to reform the starting complex. Deuteration studies were also carried out to probe the mechanism.